1. Field of the Invention
The present invention relates to air-conditioning systems and more particularly to an air-conditioning system having a cold thermal energy storage capability to reduce the direct thermal energy required for operation of the system.
2. Description of the Prior Art
The principle of using desiccants for air conditioning is widely known and numerous patents, such as U.S. Pat. Nos. 516,313 (November 1931), 2,138,684 (November 1938), 2,138,690 (November 1938), and 3,844,737 (October 1974), are found in the prior art. U.S. Pat. No. 246,626 covering desiccant absorption was granted in November 1881. A number of these patents also note the application of desiccants for direct air drying. Numerous other patents utilize the principle for air conditioning/air drying which has been known since the early 1900's and before. The last patent mentioned makes use of a regenerative zeolite desiccant wheel and a sensible heat exchanger (heat wheel). It provides a viable continuous stream of cool air. The system has been referred to in numerous papers on solar air-conditioning. Many of these presentations used solar energy plus the addition of thermal energy from gas combustion or resistance heating. The problem with these systems is that the thermal coefficient of performance is poor, normally 0.6 or lower. The thermal coefficient of performance is defined as COP.sub.Thermal =Q.sub.L /Q.sub.IN where
Q.sub.L is air-conditioning energy provided by the system, and PA1 Q.sub.IN is thermal energy required to operate the system. The energy units of both values are identical. The basic conventional absorption cycles, such as water and lithum bromide, have thermal coefficients of performance limited to approximately 0.76. PA1 a. 0.5 for one stage PA1 b. 0.95 for two stages PA1 c. 1.36 for three stages PA1 d. 1.72 for four stages PA1 e. etc.
The low coefficient of performance of these systems limits the use of direct thermal energy to produce air-conditioning economically. This is true for gas sytems, solar systems, electrical systems, and other thermal energy addition systems. However, by doubling the thermal coefficient of performance, a 50 percent reduction in the solar collector area, the major capital cost in a solar system, is possible. Reducing energy input by 50 percent or more in any air-conditioning system is obviously beneficial. This is particularly true as fossil fuel costs rise.